1. Field of the Invention
This invention relates to linearly extended devices suitable for insertion into living bodies via blood vessels and the like, and more particularly to transvenous catheters for conducting electrical pulses between the exterior of the body and the heart.
2. Description of the Prior Art
Conventional heart catheter devices comprise electrical pulse conducting elements in the form of elongated flexible members of some suitable polymeric material. Suitable flexible conductors are disposed within the insulating polymeric material to conduct electrical impulses between an electrical impulse generating means connected to the near, or proximal, end of the catheter and tissue contacting electrodes disposed at the far, or distal, end of the catheter. The electrodes are positioned on or partially embedded in the surface of the elongated catheter element. The catheter may be either unipolar, i.e., with one electrical conductor passing through it, or bipolar with two electrical conductors passing through it. There may also be an additional tension member within the elongated catheter element to provide longitudinal strength and integrity. Alternatively, a conductor or conductors passing through the catheter may provide the catheter with the requisite longitudinal strength under tension. The tension member or conductors may also provide torsional rigidity to the catheter over its length so it may be rotated by torsional force supplied at the proximal end. This enables the distal end to be rotated for better guidance as it is threaded through blood vessels and the heart chambers into final position in the lumen or interior of the heart. Catheters designed for such rotation are usually provided with a somewhat offset or bent distal end so that when the catheter is rotated, the offset end facilitates guidance of the catheter in the desired direction through the blood vessels and into the heart chambers. The ability to rotate a catheter probe is often referred to as "torque control". Also, it is desirable for the catheter probe to have a very flexible distal tip so it can be directed by the flow of blood in the venous system, such directional ability sometimes being referred to as being "floated" through the veneous system. The soft flexible distal tip of the probe also prevents trauma to the surrounding body tissues as the catheter probe is passed through the blood vessels.
Modern catheters have been conventionally formed of a polymeric material which is inert or substantially inert to body fluids. Silicon rubber, polyvinychloride, polyethylene or polyurethane may, for example, be used. The polymeric material can be extruded directly about the conductors and, if one is used, about the central tension member. Such catheters have a substantially solid cross section. Some early catheter probes were constructed of polymeric tubes within which the conductors were more or less loosely gathered. Tubular catheters having the conductors embedded in the wall of the tubing about a central lumen or channel have also been used.
Various electrodes may be used on the surface of the catheters to provide electrical contact between the interior of the heart or other intravenous structures and the conductors within the catheter. Such electrodes may be formed, for example, from rings and cups of various conductive materials resistant to body fluids. The conductors in the catheter are formed usually from thin braided or twisted, highly flexible, small diameter filaments, for example, tantalum, platinum, silver, stainless steel or other metallic materials substantially inert to body fluids. Bipolar catheters may have their proximal and distal electrodes either relatively closely or widely spaced from each other along the longitudinal extent of the catheter. Both unipolar and bipolar catheters may be provided with one or several electrodes connected to each conductor. The polymeric material of the catheter is selected or formulated and, if necessary, treated, to provide a soft, highly flexible composition in order to prevent trauma to surrounding tissues and allow easy threading and "floating" through the venous vessels into the heart chambers. Additionally the catheter, in order to provide minimum interference with the flow of blood through the venous vessels and irritation of such vessels and the heart itself, should have a very small diameter as well known to those skilled in the art. The following patents are exemplary of the state of the art summarized above.
U.S. Pat. No. 3,769,984 to Muench discloses a bipolar catheter incorporating either a cup shaped or ring type electrode at the distal end plus a ring electrode proximal thereto. The catheter may include an axial lumen which may accomodate additional apparatus including a guide wire during venous insertion.
U.S. Pat. No. 3,893,461 to Preston discloses a bipolar catheter in which the proximal electrode is significantly spaced from the distal electrode and has a surface area an order of magnitude greater than that of the distal electrode, such electrodes being embedded in a plastic member characterized as having a generally tubular form.
U.S. Pat. No. 3,903,896 to Harmjanz discloses a catheter formed from a solid core of plastic incorporating a central structural core which absorbs tensile forces. Conductors on both sides of the structural core may be contacted by compression type sleeve electrodes clamped to the surface of the catheter after removal of surface polymer material over either of the conductors.
U.S. Pat. No. 3,915,174 to Preston discloses a bipolar catheter having substantially spaced surface electrodes embedded in a plastic catheter body characterized as having a generally tubular form.
U.S. Pat. No. 3,977,411 to Hughs et al discloses a cardiac pacer system incorporating a catheter having electrodes with large and small surface areas for respectively detecting cardiac electrical potentials and electrically stimulating the cardiac tissues. The electrodes may be connected to a single or multiple electrical conductors or leads embedded in a suitable body compatible, flexible non-conductive material.
Finally, U.S. Pat. No. 4,010,755 to Preston discloses a bipolar catheter having conductors embedded in a substantially inert non-conducting casing. Two distal electrodes are used, both connected to the same conductor, and it is disclosed that the catheter could operate in a unipolar mode.
As indicated above in the known catheters, it is highly desirable that a catheter have "torque control", i.e., the ability to be rotated in a controlled manner to facilitate guidance through the venous system and correct placement in the heart chambers. Two principal methods are presently known to produce the desired properties.
One method is to embed a woven mesh material in the wall of a flexible polymeric tubing or the like. The woven mesh may be either metallic material such as stainless steel or the like or a polymeric material such as a polyester. Catheters constructed in this manner have torque control properties and may usually be rotated from any portion of the catheter, sufficient transverse rigidity being provided by the embedded mesh material to allow rotation by transversely applied torsional forces along the body of the catheter probe. This construction is expensive, however, and the rigidity of the catheter body tends to decrease flexibility and presents a possible source of trauma and irritation to adjacent tissues.
A further known method provides a single stiff wire tapered toward the end of the catheter and secured at the distal end to an end cap electrode and at the proximal end to the catheter body. This type of torque controlled catheter has excellent control when the proximal end is rotated, but the ability to transmit rotational forces applied elsewhere along the body of the catheter, for example, by manual grasping or gripping, is severly limited by the softness of the polymeric body material of the catheter.